Under the definition used herein, a multiple force-measuring device includes at least two force-measuring modules and an indicator device. The force-measuring module, in turn, includes an electromechanical force-measuring cell serving to determine a force, which functions as a measurement converter in that it converts the input quantity, which is a mechanical force, into an electrical output signal. A special type of multiple force-measuring device exists in the form of a weighing scale with a plurality of weighing devices, so-called weighing modules. The force-measuring cell is configured in this case as a weighing cell and serves for the mechanical-to-electrical conversion whereby the weight force exerted by a weighing object is converted into an electrical signal. Accordingly, a force-measuring module or a weighing module as the term is understood here means, respectively, a force-measuring device or a weighing scale without an indicator device.
A multiple force-measuring device under the terminology used herein is a force-measuring device in which the force to be measured is distributed by means of a mechanical device, in particular a measuring plate or a container, onto a plurality of force-measuring modules. Each force-measuring module in this arrangement includes a force-measuring cell, by means of which the portion of the force that is imparted to the respective module can be individually determined. The results from the individual force-measuring cells are then passed on to a common output device, where they are combined into an overall result.
Multiple force-measuring devices are used for example in industrial installations for the weighing of the contents of basins, tanks, reactor vessels and the like. Typically in these kinds of applications the weighing modules are configured as high-capacity weighing modules, as so-called tank weighing cells or reactor vessel weighing cells. For each container to be weighed, a plurality of weighing modules are arranged between the feet of the container and the foundation. Thus, each foot of the container rests on a force-measuring module. In order to determine the weight of the container and/or of its contents, the measurement values determined by the force-measuring modules need to be added, as each measurement value represents a part of the mass. This calculation is in most cases performed in a processor device and/or controller device set up in an adjacent location.
High-capacity force-measuring cells also find application as weighing modules in weighing scales for trucks. Truck scales typically have several measuring plates or weighing plates, each of which rests on a plurality of force-measuring modules. Accordingly, each force-measuring module measures a partial weight of the truck and/or of one or more trailers. The measuring results of the individual force-measuring modules are transmitted to a common processor device that is located at some distance from the measuring plates and from the force-measuring modules, for example in a controller device located as much as several hundred meters away.
According to U.S. Pat. No. 7,151,230 to Brighenti (“Brighenti '230”), the processor device is implemented as an external device in the form of a so-called weighing terminal. By way of an indicator device that belongs to the weighing terminal, the results of the multiple force-measuring device can be released. In addition, a device for supplying the multiple force-measuring device with power is arranged in the processor device. Accordingly, the individual force-measuring modules are supplied with electrical energy through this central power supply.
To transmit the measurement results and the supply current, the force-measuring modules are connected through cables to the processor device. Typically in such an arrangement, the supply current and the transmission of the measurement value are in the same cables, although by separate conductors. Furthermore, as a means to simplify the cable arrangement, the individual force-measuring modules are connected by shorter distributor lines to a distribution device, and only the latter has a direct connection through an individual cable, the so-called “home-run” cable, directly to the controller device. The power supply and the transmission of the measurement values are thus merged in the distribution device in order to avoid multiple parallel cables over the distance between the measuring plates and the controller building.
As shown in U.S. Pat. No. 5,135,062 to Lockery, if there are four force-measuring modules, the distribution device can be arranged so that it is located at the center of a rectangle formed by the four force-measuring modules. As a result, a short cable length is achieved between the force-measuring modules and the distribution device, which in consequence reduces electrical disturbances and mechanical stresses and also lowers the cost of cabling.
Particularly in larger installations, for example in weighing installations for trucks, there are often many measuring plates and force-measuring modules involved, for example four measuring plates with a total of sixteen force-measuring modules. As a result, one arrives at a multi-layered, cascaded or hierarchic network of distribution devices in order to achieve the desired merging of the connections. In the case of sixteen force-measuring modules, one ends up for example with a first level of four distribution devices, a second lever of two distribution devices, and one third-level distribution device, thus a total of seven distribution devices.
However, the distribution devices are expensive and susceptible to interference. The probability of errors in the installation process as well as during operation and maintenance increases with the rising number of components. It is therefore desirable to assemble a force-measuring device with the smallest possible number of distribution devices.
In the Brighenti '230 weighing device, eight weighing modules are connected to a central distribution device. Thus, the use of intermediate hierarchic levels of distribution devices can be dispensed with. The central distribution device serves a common juncture for the power supply as well as for the communication leads and offers the advantage of a simple arrangement of the conductor lines. Nevertheless, in most cases this arrangement involves longer distribution leads and a larger overall length of the distribution leads, thus an increased susceptibility to interference and higher costs.
To avoid these drawbacks, the cabling of the weighing modules is replaced in U.S. Pat. No. 6,919,516 to Frye by a radio transmission and individual independent power supplies of the individual weighing modules. The distribution device functions in this case as a radio relay for the transmission of the signals from the weighing modules to the processor device. Furthermore, the distribution device, too, is equipped with an independent power supply in order to eliminate all cabling. Batteries are used for the individual independent power supplies of the weighing modules and the distribution device. However, this solution has the disadvantage that the charge level of the batteries has to be checked at regular intervals, and that insufficiently charged batteries have to be recharged or exchanged. Besides, typically the performance of the batteries depends strongly on extraneous influence factors of the environment, in particular the ambient temperature. Expensive checking and monitoring activities are therefore required in order to ensure a stable, reliable operation of the weighing modules, particularly in outdoor applications.
It, therefore, an objective to propose a multiple force-measuring device, in particular a multiple weighing device, a force-measuring module, and a method of operating said multiple force-measuring device, whereby a simple and cost-effective design configuration as well as a fail-safe operation can be achieved.